Panel with decorative bark surface and method of making the same

ABSTRACT

A panel formed from a substrate such as a ligno-cellulosic board including insulation board, softwood plywood and particle board, and a protective surface for the substrate comprised of bark chips. The surface is harder than the natural, weathered bark of trees and imparts a mottled and textured surface to the substrate so that the resulting panel has superior decorative values. The method includes placing flakes and chips of bark on an adhesive coating on the face of the substrate, applying pressure to the bark to form a relatively flat surface, then abrading such surface to remove the phloem and excess chips and to relieftexture the surface.

D United States Patent 1191 1111 3,887,415 Elmendorf et'al. June 3, 1975PANEL WITH DECORATIVE BARK 2,627,375 2/1953 Grondal et a1 241/28 xSURFACE AND METHOD OF MAKING THE 3,323,935 6/1967 Snyder 156/279 X SAME3,798,098 3/1974 Ogawa et al. 156/154 [75] Inventors: Armin Elmendorf,Portola; Roland Etzold Mountain View both of Przmary ExammerGeorge F.Lesmes m Assistant Examiner-Alan T. McDonald Attorney, Agent, orFirm-Townsend and Townsend [73] Assignee: Elmendorf Research, Inc., PaloAlto, Calif.

[22] Filed: May 16, 1973 [57] ABSTRACT [21] Appl' N03 360,704 A panelformed from a substrate such as a lignocellulosic board includinginsulation board, softwood 52 US. Cl. 156/154; 117 19; 156/63; Plywoodand Particle board, and a Protective surface 5 5 5 7 5 29 for thesubstrate comprised of bark chips. The surface 161/41; 161/116; 161/162;l6l/164; is harder than the natural, weathered bark of trees and161/268; 161/27Q. 241/28 imparts a mottled and textured surface to thesub- [51] B321, 31/32; B321) 31/14; 1332b 5 strate so that the resultingpanel has superior decora- 3271 11/00 tive values. The method includesplacing flakes and 58 Field of Search 156/63, 265, 256, 264, chips ofbark on an adhesive coating on the face of the 156/276, 279 2 5 298, 3125 241/28; substrate, applying pressure to the bark to form a rela-117/16, 9 tively flat surface, then abrading such surface to remove thephloem and excess chips and to relief- [56] References Cited texture theSurface UNITED STATES PATENTS 8 Claims, 4 Drawing Figures 2,444,9297/1948 Hatch 241/28 X PANEL WITH DECORATIVE BARK SURFACE AND METHOD OFMAKING THE SAME BACKGROUND OF THE INVENTION The anatomy of bark is verycomplex and its possible uses have been only partially exploited. It iscurrently used to some extent for garden cover, mulch, fuel, andparticle boards. It is available in immense tonnage, second only involume to the residues of wood developed in the manufacture of lumberand plywood. The thick bark of softwood trees such as pines and first isparticularly useful for the process of the present invention.

For a good understanding of the present invention it is necessary toexamine bark under a microscope although some of the basic components ofbark, of importance to the present invention, can be seen without amicroscope. Reference should be made to test books on botany in whichthe following components of bark are described: Phloem, periderm,rhytidome, xylem, inner bark, stone cells, phelloderm, phellem, corkcambium, phellogen, cork cells, vascular cambium. A comprehensivediscussion of the nature of bark is given in an article by Elaine T.Howard entitled Bark Structure of the Southern Pines Wood Science, Vol.3, No. 3, January 1971.

SUMMARY OF THE INVENTION We have found that the phellogen or barkcombium is easily split by wedging action when cutting the barktangentially with a knife. It is very thin and is flanked on either sideby tissue that is hard, on the side toward the wood by thickenedunexpanded phelloderm cells and on the opposite side by stone cells. Theunexpanded hard phelloderm cells are succeeded in the direction towardthe wood by relatively weak thin-walled phelloderm cells. The hard stonecells on the opposite side of the phellogen are flanked by thin-walledcork cells. Phloem tissue follows the thin-walled phelloderm cells onthe side toward the wood and on the outer side, toward the exterior ofthe tree, it follows the thinwalled cork cells. The layers of phloemtissue are soft and relatively thick. The combined tissue between twolayers of phloem is referred to as the periderm.

The periderm is readily recognized, generally as a very thin layer, bythe naked eye. The layer of stone cells and the layer of unexpandedphelloderm are relatively hard and often differ in color from thephloem. The periderm is roughly parallel to the annual rings of the treestem. The phloem between two periderms being soft is readily crushed,whereas the cork tissue is elastic and resembles commercial cork in thisrespect. In some barks as in the firs, the cork tissue may beconspicuous. The color of the periderm varies somewhat with the speciesand with the particular tissue exposed. It differs from the color of thephloem which is generally darker. These color variations as well as thedifferences in hardness, in texture and crushability, have a bearing onthe eye appeal of the product of the present invention.

The first step in carrying out the method of the invention is to obtaina quantity of bark after it has been removed from a log. The bark ofsome pines and firs is often very thick and its anatomy lends itselfparticularly well to the process of this invention. Bark of thegymnosperms (softwoods) is generally usable while that of theangiosperms (hardwoods) is not. Bark may be removed from a log by meansof a debarking machine or a spud.

As the next step of the method, blocks of bark are reduced to thinsheets each containing at least one periderm. This can be done on a discmachine of the type used for cutting shavings of wood, or by means of agang saw. The thickness of she sheets may range from one-sixteenth inchto one-fourth inch, the cut being made approximately tangential to theperiderm. Some tearing of the phloem often takes place so that the facesmay not be entirely flat. Tearing is reduced by sawing the bark intothin sheets. While the cut may be made tangentially, radially or incross section, the tangential cut results in the most pleasing surfacein the completed product and is preferred. Moreover, compression offlakes cut tangentially requires less pressure than do flakes out eitherradially or in cross section. Crushability is needed to bring pressureon small chips between the flakes, and bonding of the small chips ishighly desirable and can only be achieved with adequate pressure.

The thin sheets of unweathered bark are next reduced in size as byflailing with swinging chains and breaking the sheets into flakes andchips, or by breaking the sheets with the hammers of a hammermill. Therelatively larger pieces of bark produced in this way have approximatelyparallel surfaces and are here referred to as flakes. The relativelysmaller pieces are here referred to as chips." Some of the chips mayhave parallel surfaces. Some phloem tissue, thin-walled cork tissue andthinwalled phelloderm may be removed in this breaking operation. Theharder tissue adjacent to the phellogen remains. The flake thickness isgenerally uniform and the faces are substantially parallel. The size ofthe flakes is effectively controlled when using a hammermill by changingthe screen size, and when using swinging chains by changing the speed ortime of flailing. Most of the flakes are relatively large, and may be upto 3 inches in size. Chips of sawdust size may be used.

Of the various conifer barks, those of the pines are preferred to carryout the method. The flakes are readily compressed, they are large, andupon removal of the phloem many flakes revealing the periderm show anirregular contour and a warped surface which adds to the attraction anddecorative effect of the completed product. A single layer of flakeswith chips in the spaces between them yields pleasing effects. Thesmaller pieces of bark produced by reducing the sheets of bark to flakesreferred to herein as chips often lean against flakes and whenuncompressed are generally without parallel faces and do not lie infixed positions on the substrate to which the flakes and chips are to bebonded; whereas, the flakes lie on one of the parallel faces.

In producing the bark facing, a heavy coat of adhesive appropriatelyextended with a filler is applied to one face of a base panel orsubstrate. The adhesive can be a coat of urea adhesive, preferablypigmented, upon which a single layer of flakes is deposited on theadhesive with open spaces between the flakes. Chips are then allowed toslip into these spaces after which chips of still smaller size are addedto fill the spaces between the chips of the first deposit. The chips ofsmaller size are deposited in excess so that some of the first depositedchips and flakes may be covered with fine material. The assembly of thebase panel with flakes and chips is vibrated to settle the chips afterwhich the assembly is subjected to pressure, preferably in a hot platepress, the pressure being maintained until the adhesive has set.Adhesives that set at room temperature may also be used.

As substantially all flakes are partly composed of soft phloem or softperiderm tissue, they may be compressed. The pressure applied isadequate to compress the flakes to the point where some pressure istaken up by the chips between the flakes so that the small chips incontact with the adhesive are bonded as well as the large flakes. Thesmall chips not in contact with the adhesive are subsequently removed bywire brushing. In this manner the base panel is provided with a singlelayer of large flakes and chips all of which are firmly bonded to thebase panel so that the surface of the panel is completely covered withbark in a single layer.

The panel having the unabraded surface with which it leaves the pressmay also be used for decorative purposes, even though it lacks therelief texture resulting from wire brushing. It incorporates the mottledappearance and wear differences inherent in different flakes that arenot weathered.

By wire-brushing or sandblasting the bark surface, most of the phloemtissue and the soft phelloderm and phellem tissue of the periderm areremoved thereby exposing the harder pheloderm cells and stone cells. Theresultant panel surface is harder and much more scratch resistant thanthe original bark surface of the tree.

In flakes where the layers of hard cells of the periderm are exposed thesurface of the flake often takes on a luster which enhances thedecorative value of the panel. Where phloem tissue remains attached toflakes, there, light will reflect different than from the glossysurfaces. A further feature of the bark surface that contributes to eyeappeal lies in the fact that the exposed periderm surfaces lie indifferent planes, so that texture is enhanced. The surfaces of thebrushed flakes may lie in planes that are slightly tilted in respect toeach other, thereby adding variety to the panel surface, and socontributing to the mottled appearance.

Some barks are rich in cork which shows as streaks of yellow in thepredominant reddish brown color of the flakes. Some differences in shadealso show in the predominant color of the flakes. These may take on apurplish hue or a tinge of grey. From this it will be seen that greatvariety exists in the natural bark color and texture resulting fromremoving soft tissue and exposing underlying harder tissue.

The compressibility and crushability of the phloem and of thethin-walled phelloderm cells have bearing on the pressure required forbonding the flakes, but the hardness of the substrate used must also beconsidered in determining the pressure for good bonding. Soft boards ofthe insulation board type are readily indented and are preferred toharder products such as plywood and particle boards. Short time, hotplate pressures up to 100 psi generally do not compress insulationboards unduly. The hardness of the surface of bark on board productsafter wire-brushing to remove soft tissue always exceeds the hardness ofthe original uncompressed and nonabraded bark and exceeds therequirement of scratch resistance in wall paneling.

While bark of conifers is preferred, and particularly that of pine, barkof some genera of conifers is stringy or fibrous such as that ofredwoods and cedars and tends to be pulverized in failing. Barks thatare fibrous are, therefore, unsatisfactory.

In place of depositing the flakes and chips on a substrate, they may bedeposited as a thick bed of flakes and chips, each of which have beencoated with an adhesive as in conventional particle board manufacture.Upon removal from the press, the resulting flat surface can be brushedto remove soft tissue, leaving the harder tissue exposed as in the casepreviously described in which a separately manufactured substrate isused. The bonding together of the flakes in the bed of such a panel andthe bonding of the surface flakes and chips to this bed take placesimultaneously.

The primary object of this invention is to provide a decorative paneland method of making the same wherein the panel has a surface formed ofunweathered bark arranged in a manner to provide an attractiveappearance permitting the panel to be used for decorative purposes.

Another object of this invention is to provide a panel as describedwhich has a number of relatively large flakes of bark and a number ofrelatively small chips of bark adhering to one face of a substrate andhaving irregular mottled surfaces formed by removing portions of thephloem from the outer faces thereof to provide the decorative appearancefor the panel and to present a surface which is harder than the natural,weathered bark of trees.

A further object of this invention is to provide a method for making thedecorative panel as described wherein flakes and chips of bark aredeposited on an adhesive coated surface of a substrate and compressed toform a relatively flat surface which is thereafter abraded to remove theouter phloem of the flakes and chips to produce a textured, mottled faceand thereby to provide a relief-textured surface.

Other objects of this invention will become apparent as the followingspecification progresses, reference being made to the accompanyingdrawing for an illustration of the panel.

In the drawing:

FIG. 1 is a vertical section through a plywood substrate having a layerof flakes and chips of bark on an adhesive coated surface thereof:

FIG. 2 is a view similar to FIG. 1, showing the same assembly betweenthe platens of a hot press;

FIG. 3 is a view similar to FIGS. 1 and 2 but showing insulation boardas the substrate with the upper surface of the board indented due to thepressured applied to the bark flakes and chips and after the flatsurface of the bark has been abraded; and

FIG. 4 is a perspective view of a portion of a panel obtained bycarrying out the method of the invention.

To illustrate the method of the invention, reference is made to FIGS. 1and 2 which show a base panel or substrate 1 which can be anyligno-cellulosic panel such as insulation board, plywood, particle boardand even paper. In FIGS. 1 and 2, the substrate is plywood. Base panel 1is provided with a coating 2 of a heavy bodied adhesive. A number ofselectively large flakes of bark 3, 4 and 5 are first deposited oncoating 2 and are spaced apart as shown in FIG. 1. Each flake has atleast one periderm 3a. However, for purposes of illustration, a numberof periderms are shown for each flake. Between the periderms is thephloem 3b.

Next, relatively small bark chips 6, 7 and 8 are deposited in the spacesbetween flakes 3, 4 and S, the chips being smaller than the flakes andfitting in open spaces 9 between the flakes essentially to fill suchopen spaces. Each chip can contain one or more periderms, with thematerial on the opposite sides of each periderm consisting of phloem. Anexcess of chips is generally applied to completely fill spaces 9although such excess is not illustrated in FIG. 1. The assembly of thesubstrate, flakes and chips is then placed in a hot press 26 (FIG. 2)comprised of a lower plate 24 and upper plate 25. The press appliespressure to the assembly as shown in FIG. 2 to compress the flakes 3, 4and 5 sufficiently to bring some pressure on chips 6, 7 and 8. Thecompression also operates to bond the flakes and chips to thesubstrate 1. The flakes are compressible primarily due to the presenceof relatively thick phloem. When taken from the press, the assembly hasa generally, flat, upper surface. When an insulation board is used asthe substrate, the upper surface of the substrate is indented by flakesand chips under pressure as shown in FIG. 3.

The next step of the method is to abrade the flat, upper surface of theexposed assembly, as by a rotating steel brush. This action removesphloem 30 (FIG. 2) and soft portions of periderm and excess unbondedchips, resulting in a relief-textured surface of the type shown in FIG.3. The panel is then completed and can be readily used in a wide varietyof different decorative applications as, for example, a wall panel. FIG.4 shows the completed panel in perspective and illustrates the relative.sizes of the flakes with respect to the chips therebetween. We claim: 1.A method of producing a panel having decorative bark facing whichcomprises the following steps:

placing bark flakes and chips on an adhesive-coated ligno-cellulosicsubstrate in a single layer; and

applying pressure and compressing the flakes until pressure is exertedonto most of both the flakes and the chips and until both are bonded tothe substrate in a single layer.

2. A method as set forth in claim I, wherein is included the step ofabrading the bark surface, after said surface has been bonded to thesubstrate, to remove soft tissue from the flakes and the chips.

3. A method as set forth in claim 1, wherein said substrate comprises aligno-cellulosic board of the insulation board type, and wherein thethicker ones of said flakes and chips are partly embedded during saidpressure applying step.

4. A method as set forth in claim 1, wherein said substrate is comprisedof a bed of adhesive-coated bark flakes and chips.

5. The method of producing a decorative bark facing for aligno-cellulosic board which includes the following steps:

reducing bark of conifers generally tangentially to flakes and chips,the flakes containing at least one periderm layer, the periderm layerbeing generally parallel to the facets of the flakes, and the chipsbeing smaller in size than the flakes;

placing the flakes on the adhesive of an adhesive coated substrate withspaces between the flakes; introducing chips in the spaces;

applying pressure and compressing the flakes until pressure is exertedonto most flakes and chips; and bonding the flakes and chips to thepanel.

6. The method as set forth in claim 5, wherein is included the step ofabrading the entire bark surface after said bonding step and removingphloem, thin-walled cork tissue and expanded phelloderm tissue as wellas less well-bonded chips.

7. A method as set forth in claim 5, wherein is included the steps ofcompressing the flakes and chips beyond their elastic limit, abradingthe entire surface to remove all soft and loose material from the sameto thereby expose hard, densified, irregularly-shaped periderm layers.

8. A method of producing a hard, decorative bark facing on aligno-cellulosic substrate which includes in part the following steps:

placing bark flakes in a single layer on an adhesivecoated substratewith open spaces between the flakes;

depositing bark chips in two or more layers onto the surface with mostof the chips in the spaces between the flakes;

applying pressure to compress the flakes until pressure is exerted ontoall of the flakes and chips in contact with the adhesive coat;

maintaining the pressure until all the flakes and chips in contact withthe adhesive coat are bonded to the substrate in substantially a singlelayer; and abrading the surface to remove the chips not bonded to thesubstrate and to remove soft tissue from the flakes and chips bonded tothe substrate.

1. A method of producing a panel having decorative bark facing whichcomprises the following steps: placing bark flakes and chips on anadhesive-coated ligno-cellulosic substrate in a single layer; andapplying pressure and compressing the flakes until pressure is exertedonto most of both the flakes and the chips and until both are bonded tothe substrate in a single layer.
 1. A method of producing a panel havingdecorative bark facing which comprises the following steps: placing barkflakes and chips on an adhesive-coated lignocellulosic substrate in asingle layer; and applying pressure and compressing the flakes untilpressure is exerted onto most of both the flakes and the chips and untilboth are bonded to the substrate in a single layer.
 2. A method as setforth in claim 1, wherein is included the step of abrading the barksurface, after said surface has been bonded to the substrate, to removesoft tissue from the flakes and the chips.
 3. A method as set forth inclaim 1, wherein said substrate comprises a ligno-cellulosic board ofthe insulation board type, and wherein the thicker ones of said flakesand chips are partly embedded during said pressure applying step.
 4. Amethod as set forth in claim 1, wherein said substrate is comprised of abed of adhesive-coated bark flakes and chips.
 5. The method of producinga decorative bark facing for a ligno-cellulosic board which includes thefollowing steps: reducing bark of conifers generally tangentially toflakes and chips, the flakes containing at least one periderm layer, theperiderm layer being generally parallel to the facets of the flakes, andthe chips being smaller in size than the flakes; placing the flakes onthe adhesive of an adhesive coated substrate with spaces between theflakes; introducing chips in the spaces; applying pressure andcompressing the flakes until pressure is exerted onto most flakes andchips; and bonding the flakes and chips to the panel.
 6. The method asset forth in claim 5, wherein is included the step of abrading theentire bark surface after said bonding step and removing phloem,thin-walled cork tissue and expanded phelloderm tissue as well as lesswell-bonded chips.
 7. A method as set forth in claim 5, wherein isincluded the steps of compressing the flakes and chips beyond theirelastic limit, abrading the entire surface to remove all soft and loosematerial from the same to thereby expose hard, densified,irregularly-shaped periderm layers.
 8. A method of producing a hard,decorative bark facing on a ligno-cellulosic substrate which includes inpart the following steps: placing bark flakes in a single layer on anadhesive-coated substrate with open spaces between the flakes;depositing bark chips in two or more layers onto the surface with mostof the chips in the spaces between the flakes; applying pressure tocompress the flakes until pressure is exerted onto all of the flakes andchips in contact with the adhesive coat; maintaining the pressure untilall the flakes and chips in contact with the adhesive coat are bonded tothe substrate in substantially a single layer; and abrading the surfaceto remove the chips not bonded to the substrate and to remove softtissue from the flakes and chips bonded to the substrate.